Raw powders to be used for production of low alloys steels having an excellent hardenability by powder metallurgy

ABSTRACT

Raw powders to be used for production of low alloy steels having an excellent hardenability by powder metallurgy consist of 0.902.50% by weight of Mn, 0.35-1.50% by weight of Cr, 0.10-1.00% by weight of Mo, not more than 0.10% by weight of Si and remainder substantially being Fe, provided that the sum of Mn and Cr is 1.70-3.10% by weight. When 0.10-1.00% by weight of Ni is additionally added thereto the hardenability is further improved.

United States Patent Ito et a]. June 17, 1975 RAW POWDERS TO BE USED FOR [56] References Cited PRODUCTION OF LOW ALLOYS STEELS UNITED STATES PATENTS HAVING AN EXCELLENT 2,284,638 6/!942 Clark et al Is/0.5 BA HARDENABILITY BY POWDER 3.687.654 8/1972 Huseby 75/05 PA METALLURGY 3,798,022 3/1974 LeBrasse 75/05 BA 3,837,845 9/:974 Church .7 15/05 BA Inventors: Shunji Ito, Chiba; Yasual-ti Morioka, Ohami; Yoshihiro Kajinaga; Minoru Nitta, both of Chiba; lchio Sakurada, lchihara, all of Japan Assignee:

Filed:

pan

July 1, 1974 Appl No.: 484,945

Kawasaki Steel Corporation, Kobe,

Primary Examiner-W. Stallard [57] ABSTRACT Raw powders to be used for production of low alloy steels having an excellent hardenability by powder metallurgy consist of 0.902.50% by weight of Mn, ().35l 50% by weight of Cr, 0.]-1 .00% by weight of Mo, not more than 0.10% by weight of Si and remainder substantially being Fe, provided that the sum of Mn and Cr is l.703.l0% by weight. When 0.l0-l.00% by weight of Ni is additionally added July Japan 48'75299 thereto the hardenability is further improved.

ll?8ft:1:53:31;Jjjjjjjjjjijjjjjj.Yiilliifffiiil3%? 6 Claims, 5 Drawing Figures Field of Search 75/05 BA, 0.5 R, 0.5 C, 75/05 B, I26 C Q 50,- g 45 g 40 b b I 35 E 30 P i 25 U Q I0 L l I 1 I 4 i 1 l 1 Distance from the Quenched End (mm) PATENTEDJUN 17 ms 3 90,1335 we; 1

FIG. I

U 35 E30- E25- 8 [0 l n I l 1 1 l 1 J Distance from the Quenched End (mm) PATENTEDJUN 17 1975 Distance from the Quenched End (mm) PATENTEDJUN 17 ms Rockwell Hardness (HRC) a a 8 g PATENTEDJUN 17 ms L? l,

SEEU 4 mu Qua Rockwell Hardness HR 6) m Q o 5 15/5 5025303540455055 Distance from the Ouenched End (mm) PATENTEDJUNI? ms 3 590,135

Distance from the Quenched End (mm) RAW POWDERS TO BE USED FOR PRODUCTION OF LOW ALLOYS STEELS HAVING AN EXCELLENT HARDENABILITY BY POWDER METALLURGY The present invention relates to the raw powders to be used for production of low alloy steels by powder metallurgy and particularly the raw powders to be used for production of automobile parts through the socalled sinter forging.

Recently. the sinter forging has been noticed in the powder metallurgy but there are many problems to be solved. so that the sinter forging has never been industrially carried out. The most important problem among them is the raw powders themselves to be used and particularly the raw materials which have taken the hardenability and the mechanical properties of the product produced by the sinter forging into consideration, have never yet been proposed.

Those which are applied to the sinter forging, are automobile parts and these parts require abrasion resistance, toughness and other mechanical properties and necessarily the excellent hardenability is needed. For example, even in the case of automobile parts presently used, which are made by machining the bar stock, the final qualities are determined by the heat treatment and also on the parts subjected to the sinter forging which can omit many machining steps, the final qualities are naturally determined by the heat treatment.

The inventors have investigated the reason why the raw powders having the above described properties cannot be obtained and found the following facts.

a. Since the raw materials are powder, the specific surface area is large. Namely, the raw powders have a larger specific surface area than the molded products having the same volume and consequently the amount of oxygen increases. For example, even in the case of pure iron powders fully reduced, about 0.3% by weight of oxygen is usually contained and this value is much larger than rimmed steel 0.020.03%} and killed steel (0 0.0l%).

Accordingly, the large amount of oxygen impairs the hardenability and deteriorates the mechanical properties.

b. In general, Cr, Mn and the like improve the hardenability as the molding materials but these elements may impair the hardenability in the sinter forging.

Namely, Cr and Mn are elements easily oxidized and are apt to form oxides. Furthermore, when the oxides of these elements are once formed, these oxides are difficult in the reduction and consequently the amount of oxygen increases and the inherent activity for improving the hardenability of Cr, Mn and the like cannot be developed and rather the contained non-metal inclu sion increases, whereby the mechanical properties are deteriorated.

Thus, it has usually made an effort to add Mn and Cr in content as low as possible to prepare the raw powders and this is apparent from A] 4600 powder (Mn: about 0.3%, Ni: about 2%, Mo: about 0.5%, remainder: Fe) and A15] 8600 powder (Mn: about 0.5%, Ni: about 0.5%, Cr: about 0.5%, Mo: about 0.5%, remainder: Fe).

As mentioned above, the conventional raw powders have various problems and the present invention aims at to solve these problems.

The present invention consists in the raw powders to be used for the production of low alloy steels having an excellent hardenability by powder metallurgy, which consist of 0.902.5% by weight of Mn, 0.35-1.50?! by weight of Cr. (HO-1.00% by weight of Mo, not more than 0.10% by weight of Si and the remainder substantially being Fe, provided that the sum of Mn and Cr is 1.70-3. l0% by weight.

The reason for defining the composition of the powders of the present invention will be explained in the following.

USO-2.50% by weight of Mn Mn is an element for improving the hardenability and in the present invention, this element is added for such a purpose. In less than 0.90% of Mn, the effect for improving the hardenability is low, so that the lower limit of Mn is defined to be 0.90%. lt is preferable in view of the hardenability that the Mn content is larger but the present invention is characterized in that the improvement of the hardenability is attained by the coexistence of the defined amounts of Mo and Cr. Therefore, the Mn content has the upper limit in view of the hardenability and when said content exceeds 2.50%, the hardenability is rather deteriorated. Furthermore, when the Mn content exceeds 2.50%, the oxygen content abnormally increases and the powder granules themselves become hard, so that the cold compactibility becomes difficult. 0.35l.50% by weight of Cr Cr is an element which contributes to the improvement of the hardenability together with Mn and Mo. Thus, it is necessary to determine the Cr content in relation to the contents of Mn and M0. The lower limit of the Cr content is 0.35% in view of the hardenability. The upper limit of the Cr content should be determined from this view but when the Cr content is large, the viscosity of the molten steel becomes high and unless the temperature is raised abnormally, the atomizing nozzle before granulation is clogged, the oxygen content increases and the cold compactibility of the powders becomes difficult, so that the upper limit of Cr is defined to be 1.50% by weight.

0. l0-l 00% by weight of Mo It has been shown that M0 is an element which is ef' fective for the improvement of the hardenability, the annealing resistance, the annealing brittleness and the like, but the present invention is characterized in that it is noticed that M0 is an element which improves and promotes the hardenability owing to Mn and Cr. However, M0 is expensive and therefore it is necessary to define the range of M0 in economical and effective view. From this point, the Mo content must be 0. l0-l 00% by weight in relation to the amounts of Mn and Cr. l.703.l0% by weight of Mn-l-Cr The lower limit of the sum amount of Mn and Cr must be l.70% in view of the hardenability within the range of 0.902.50% of Mn and 0.35l.50% of Cr.

Even if it is preferable in view of the hardenability that the sum amount of Mn and Cr is larger, when said amount is too large, the oxygen content of the powder increases and rather the hardenability is deteriorated and further the mechanical properties are impaired, so that the upper limit of the sum amount of Mn and Cr is defined to be 3.10%. Moreover, when the sum amount of Mn and Cr exceeds 3. l0%, the hardness of the powder granules themselves increases and the cold compactibility of the powders becomes difficult. This is also the reason of the definition.

The above mentioned Mn, Cr and Mo are the elements which develop the effect by positively existing. while it is preferable that Si rather is not present.

Thus, Si is a negative element in the present invention.

Therefore, in the present invention, Si is not particularly added different from the case of the usual molded steel and the amount of Si inevitably allyed is not more than 0.10% by weight.

Furthermore, Si is a negative element in view of the hardenability in the present invention and less Si contributes to the improvement of the hardenability together with the above mentioned positive elements of Mn, Cr and Mo. Particularly, in this case. only when Si is not more than 010%, if Cr, Mo and Mn are within the above described ranges, the effect of Si can be de veloped to the largest extent.

Remainder of Fe The remainder does not consist of only Fe but con sists substantially of Fe and contains impurities in such an extent as in usual steels (powder, molded steel). Accordingly, this is the same with respect to C and C is about 0.2% by weight when used as a case-hardening steel and C is about 0.4% when used as tempering steel.

The powders of the present invention consist of the composition as mentioned in detail hereinbefore, but in this composition, when a part of the remainder of Fe is substituted with Ni, the effect for improving the hardenability can be more improved.

010-1009"? by weight of Ni It has been usually considered that Ni is an element which does not contribute to the hardenability. However, it has been found that when the Si content is low and further the amount of Mn is high and Cr and Mo coexist, Ni can improve the hardenability noticeably. Furthermore, Ni improves the reducibility and even if Mn and Cr are contained in a large amount, the presence of Ni can lower the oxygen content considerably.

The above described effect of Ni will be understood through Example mentioned hereinafter but an explanation will be made with respect to the effect of Ni as follows.

FIG. 1 relates to the powders of the present invention and when the powders of A. B and C are compared with the powders of A, B and C, in the former powders of A. B and C, Ni is particularly added and it can be seen that the oxygen contents in these powders are more reduced and the harden-abilities in these powders are more improved than those in the powders ofA', B and C. In addition, Ni makes fine grain structure and consequently even if the cementation or the heat treatment are effected after the sinter forging, the structure does not become coarse and this contributes to the improvement of the mechanical properties.

Accordingly, it is preferable in the present invention to add Ni and it is necessary to add at least 0.10% by \veight of Ni in order to attain the effect of the addition of Ni. However, even if the amount of Ni added in creases, the effect cannot be increased in relation to the increased amount and a too large amount of Ni is not economic and rather increases the retained austenite amount. so that the upper limit of Ni is l.00% by weight.

By preparing the raw powders from the above described composition, the powders of the present invention can be obtained.

These powders can be produced. for example, by granulating the raw powders by atomizing process and other conventional processes and then, for example, subjecting to a reduction annealing under hydrogen atmosphere.

For a better understanding of the invention, reference is taken to the accompanying drawings:

FIG. 1 is a diagram showing .lominy curves of the powders according to the present invention;

FIGS. 2 and 3 are diagrams showing Jominy curves of the comparative powders; and

FlGS. 4 and 5 are diagrams showing Jominy curves of the well known powders.

The invention will be explained with respect to examples but is not intended to limit thereto.

The powders of the composition as shown in the following Table l were produced by water atomizing process and after granulation, the granules were subjected to a reduction annealing under hydrogen atmosphere at l,()50C for 3 hours.

in the powders in Table l, A-C' are within the scope of the present invention and E-K are the comparative powders. The powders A-K were almost composed of about l7% of lOO-lSO mesh powder about 28% of [50-200 mesh powder about l5% of 200250 mesh powder about [5% of 250325 mesh powder and about 25% of minus 325 mesh powder and there is no great difference in the particle size distribution of each powder.

The powders A-K were prepared as mentioned above and these powders and the powders having the composition as shown in the following Table 2 were compacted under a pressure of 5 t/cm to obtain the green compacts having a density of 6.5 g/cm, which were sintered under the endothermic gas (propane-air cracking gas) at l,()5()C for l hour and then the sintered bodies were heated at l,200C for 5 minutes under hydrogen atmosphere and was forged in a die under a pressure of IO tlcm By such a sinter forging, steel blocks having a density of more than 99.5% were obtained. These steel blocks were normalized at 870C following to MS G056l and then worked into Jominy test samples. These samples were subjected to a one end quenching test at 845C. The amount of carbon in Tables I and 2 is an analized value of the samples remained after the above described test and the other components are the analized values of the powders themselves. The results of the quenching test are shown.

Table l C Si Mn Ni Cr Mo 0 Steel powder lVr] ['71 l (71 1 t'fr' ('4 1 ("fr I (/l Component system Present invention Example I A 0.43 0034 l.4l 0.54 0.54 0.58 0.15 Si not added, MnNi-Cr-Mo Example 2 B 041 0.0l0 0.98 0.h2 0H8 0.14 0.20 Si not added. Mn-Ni-Cr-Mo Example 3 C 0.37 0.007 lflh 0.8) 0.4] 0.7% (U7 Si not added. Mn-Ni-(rMo Example 4 A 0.3) 0.02) L34 0.03 (I 44 0.60 0.31 Si not added. Mn-(r-Mo [-xnmple 5 B 0.3) (Hill 0 0.04 I05 0.12 0.24 Si not added. Mn-(r-Mo Example (1 C 0.38 0.023 1.87 0.0} 0.17 0.6 0.33 Si not added. Mn-LrMo Table l (ontinued Si Mn Ni (1' Mo Steel powder (-4 I ('1 I ('21 (1' ("I ('i ("I I Component system Comparative Example 7 li 0.41 0.015 1.39 0.02 0.5.1 0.021 0.31% Si not added. Mn-(r Example K I" 0.35 0.22 1.23 0.01 0.61 0.4- 0.43 Si-Mii-('r-Mo lixamplc 1 (i 0.38 0.31 1.37 (I 30 0.47 0.00 0.35 Si-Mn-Nilr-Mo [:Ixamplc H 0.47 0.038 0.78 0.7-1 0.01 0.0} 0.19 Si not zlddcd. MlrNi-Mo lzxamplc l l I 0.44 0.021 3.02 0.71 0,3) 049 0.02 Si not added. Mn-Ni t'r Mo Iixaniple I2 I 0.36 0.04. 1.31 0.30 2.34 0 51 0.2-1. Si not added. Mn-Ni-(rMo Izxample 13 K 0.43 0.072 1.25 1.113 0.38 0.3-1 0.21 Si not added. MwNilrMo Table 2 Si Mn Ni (r Mo Steel powder 5 J [94) 1% (I7! (9 ('71 I (U? Component system Conventional alloy steel powder L 0.37-0.45 11.20-41.35 0.701.115 0.80-1.15 0.15 0.25 Si containing SAE 4140 H M 0.37-0.45 0.10-0.35 0.70 .05 0.354).?5 (135-0115 01541.25 Si containing SAE 8640 H N 0.37-0.45 0.20-0.35 0.60-0.95 l.50 2.00 0.05-0.95 0.200.30 Si containing SAIi 4340 H 0.59 0.48 0.5' low Mn-Mo (Japanese Patent laid open No. 20.049/72] P 0.39 0.020 0.54 0.511 0.42 0.45 0.46 low MnNi'Cr-Mo. AISI 8600 Q 0.47 0.010 0.28 1.01 0.02 0.45 0.25 low MnNi M0. AISI 4600 The powders of A, B and C do not substantially contain Ni. In A. B and C. the hardenability is more improved than those of FIGS. 2 and 3 but is more or less inferior to that in A. B and C. which contain Ni.

When the amounts of Mn and Mo are lower. that is 0.90-1.6570 by weight of Mn and (no-0.30% by weight of Mo, the hardening depth of the quenching hardness curve becomes more or less shallow but the curve takes such a form that the hardness decreases gradually from the quenching end towards the interior. The materials having such a property are most suitable for parts in which the fatigue strength is important.

On the other hand, when Mn and Mo are higher, that is l.l02.50% by weight of Mn and 0.201.00% by weight of M0, the quenching hardness curves takes such a form that the hardness lowers rapidly at a certain distance from the quenched end. The materials having such a property are most suitable for parts which need an enough impact toughness.

When the results in FIG. 2 are compared with those in FIG. 1, the composition of A can be compared with the composition ot'G and the composition of A can be compared with the composition of F. From this comparison, it can be seen that the compositions of G and F are higher in the Si content than the defined Si content in the present invention and when Si is more than 0.10%, the oxygen content increases as shown in Table 1 and the hardenability is deteriorated. With reference to FIGS. 1 and 2, when the composition of A is compared with the composition of E, the composition of E is within the scope of the present invention in the amount of Mn. Cr and Si but the Mo content is lower than the defined content of Mo in the present invention and the hardenability in E is inferior to that of A. From this fact, it is apparent that the improvement of the hardenability of the powder does not coincide with the prior metallurgical common sense and relies upon the coexistence of Cr. Mn and Mo under such a condition that the amount of Si is not more than 0.10%.

When the composition of H is compared with the compositions of A(" according to the present invention. the former is very low Cr content. From the comparison with the data in FIG. 1 and those in FIG. 2, it can be seen that the defined content of Cr is essential as one of the coexisting elements.

The composition ofl is higher in the Mn content than the compositions of AC' according to the present invention and the composition of J is higher in the Cr content than the compositions of A-C' and as seen from Table I. the compositions ofl and .I are higher in the oxygen content and as seen from FIG. 3 the hardenabilities of these compositions are lower and the mechanical properties are poor and the cold compactibility of the powders lowers.

In the composition I having a large content of Cr. the viscosity in the molten steel was high and the atomizing nozzle was clogged upon the atomizing step.

The composition of K is too large in the Ni content and in this composition, the retained austenite amount increases, so that the hardness at the quenched end decreases as shown in FIG. 3 and the oxygen content is comparatively high as shown in Table I. This shows that although Ni has the above described effect but there is an optimum range.

The hardening depth of the above described comparative tests is as follows.

AC' in FIG. 1 are compared with E. F, G and H in FIG. 2. In both the FIGS. 1 and 2, the hardnesses at the quenched end are substantially same but the powders in FIG. 2 are poor in the hardening depth. Each element in these powders will be checked. In the composition of E, the Si content is as low as 0.015% but also the Mo content is as low as 0.021%. so that the hardenability is poor. In the compositions of F and G. the Si content is 0.22% and 0.31% respectively and is high and in the composition of F, the Ni content is as low as 0.01%, while in the composition of G. the amount of Ni is 0.36% and is within the scope of the present invention. but the influence of the addition of Si is high and the hardenability is poor. In the composition of H. the amount of Si content is low but also Cr is as low as 0.01%, so that in this powder, the hardenability is poor,

When the data in FIG. 3 showing the powders of l, J and K are compared with those in FIG. 1 showing the powders of the present invention. the powders in FIG. 3 are lower in the hardeness at the quenched end and the hardening depths of these powders are not very good.

The behavior of each element of the powders according to the present invention will be understood. Furthermore, the data concerning the well known powders are shown in FIGS. 4 and S.

In Table 2, any of the powders of LN contain 0.20-0.3570 of Si, the powder ofO does not contain Si nor contain Ni and Cr. The powder of P is low in the Mn content and the powder ofQ is low in the Mn content and is too high in the Ni content and too low in the Cr content.

All the powders of L, M and N contains more than 0.10% of Si and the effect of coexistence of Mn, Cr and Mo and the effect of additionally adding Ni thereto are not developed and therefore the hardenability is not improved.

The effect of the powders of the present invention will be understood through the explanation in the above Example. If an explanation is made with respect to the carbon content and the hardening depth in the powders of the present invention, it can be considered that the powders are utilized for tempering steel and casehardening steel, In the case of using the powder for tempering steel, the carbon content is about 0.4% and it is characterized that the hardness of mm and mm from the quenched end is more than 50 in Rockwell C scale and more than 40 in said scale respectively and particularly the hardness is not rapidly varied at the zone of 10-15 mm from the quenched end.

We claim:

1. Raw powders to be used for production of low alloy steels having an excellent hardenability by powder metallurgy, which consisting mainly of 0.90-2.50% by weight of Mn, 0.351.50% by weight of Cr, 0. {04.00% by weight of Mo, not more than 0.10% by weight of Si and remainder substantially being Fe, provided that the sum of Mn and Cr is l.703.l0% by weight.

2. Raw powders to be used for production of low alloy steels having an excellent hardenability by powder metallurgy, which consisting mainly of 0.902.50% by weight of Mn, 0.35] 50% by weight of Cr, 0.l01.00"/Z by weight of Mo, O.l0l.00% by weight of Ni, not more than 0.10% by weight of Si and remainder substantially being Fe, provided that the sum of Mn and Cr is l.703.10% by weight.

3. The raw powders as claimed in claim 1, wherein Mn is 090-16570 by weight and M0 is 0.l00.80% by weight.

4. The raw powders as claimed in claim 1, wherein Mn is 1.l02.50% by weight and M0 is 0.201.00% by weight.

5. The raw powders as claimed in claim 2, wherein Mn is 0.90-1.65lv by weight and M0 is O.100.80% by weight.

6. The raw powders as claimed in claim 2, wherein Mn is l,l02.50% by weight and Mo is 0.20l.00% by weight. 

1. RAW POWDERS TO BE USED FOR PRODUCTION OF LOW ALLOY STEELS HAVING AN EXCELLENT HARDENABILITY BY POWDER METALLURGY, WHICH CONSISTING MAINLY OF 0.90-2.50% BY WEIGHT OF MN, 0.35-1.50% BY WEIGHT OF CR, 0.10-1.00% BY WEIGHT OF MO, NOT MORE THAN 0.10% BY WEIGHT OF SI AND REMAINDER SUBSTANTIALLY BEING FE, PROVIDED THAT THE SUM OF MN AND CR IS 1.70-3.10% BY WEIGHT.
 2. Raw powders to be used for production of low alloy steels having an excellent hardenability by powder metallurgy, which consisting mainly of 0.90-2.50% by weight of Mn, 0.35-1.50% by weight of Cr, 0.10-1.00% by weight of Mo, 0.10-1.00% by weight of Ni, not more than 0.10% by weight of Si and remainder substantially being Fe, provided that the sum of Mn and Cr is 1.70-3.10% by weight.
 3. The raw powders as claimed in claim 1, wherein Mn is 0.90-1.65% by weight and Mo is 0.10-0.80% by weight.
 4. The raw powders as claimed in claim 1, wherein Mn is 1.10-2.50% by weight and Mo is 0.20-1.00% by weight.
 5. The raw powders as claimed in claim 2, wherein Mn is 0.90-1.65% by weight and Mo is 0.10-0.80% by weight.
 6. The raw powders as claimed in claim 2, wherein Mn is 1.10-2.50% by weight and Mo is 0.20-1.00% by weight. 